(1) Field of the Invention
This invention relates generally to a keyboard switch and more particularly to an improved thin type keyboard switch suited for use with notebook type personal computers.
(2) Description of the Prior Art
In a thin type keyboard switch, in order to improve operability, the keytop is usually slanted with the front edge side, which is nearer to an operator, slightly lower than the rear edge side.
A variety of mechanisms which enable smooth vertical displacement of these keytops have been proposed. One of these mechanisms utilizes a crosslink.
As shown in FIG. 9, this crosslink 13 arrangement includes central fulcrums 16, a first link arrangement 14 composed of two parallel links connected to a transverse member, and a second link arrangement 15 composed similarly of two parallel links connected with another transverse member. Right and left fixed fulcrums 17 and 17, are located at one end of each of the links of the first link arrangement 14, while traveling or moving fulcrums 18 and 18, are located at the other end of the links of the second link arrangement 15. These moving fulcrums 18, 18 engage the frame 11 in such a fashion that they can be displaced horizontally with respect thereto. In addition, right and left fulcrums 20 and 20 on the other ends of the links of the first link arrangement 14, are supported on the lower face of the keytop 12 so that they may be displaced horizontally, while right and left fulcrums 19 and 19 on the other end of the links of the second link arrangement 15, are pivotably supported on the lower face of the keytop 12.
In the crosslink 13 of the conventional keyboard switch 10, the ratio of the left to right length (a:b) of the first link arrangement 14 as divided by the rotatable fulcrum 16, is almost 1:1 as shown in FIGS. 8A and 8B. Similarly, the ratio of left to right length (c:d) of the second link arrangement 15 as divided by the rotatable fulcrum 16, is almost 1:1 also as shown in FIGS. 8A and 8B. Thus, the fulcrums 17, 18, 20, and 19 are located in a manner which outlines a parallelogram.
In such a crosslink 13, which outlines the parallelogram, the fulcrums 18 and 20 displace horizontally while approaching one another as the keytop is pushed down, which the keytop 12 remains slanted as it descends. At that time, the front edge side 32 of the keytop 12 reduces to a height of h2, while the rear edge side 33, whose original height was H0, only lowers to a height of h1.
Thus, the top face of the keytop 12, which is slanted with the lower front edge side 32 and higher rear edge side 33, facilitates visual recognition of the characters on the respective keys of a keyboard and improves the operablilty of the same.
In the foregoing conventional keyboard switch 10, however, the keytop 12 is pushed down while still slanted. The height of the keytop 12 may therefore be decreased only to h1. The thickness of the notebook type personal computer which utilizes this type of keyboard switch is thus limited. Therefore, particularly in a conventional notebook type personal computer with a display mounted in its lid, the thinness of the notebook with all the keytops 12 pushed down, has been limited when the lid is closed.
The character printing which is carried out using a silk screen technique, for instance, is provided on each keytop 12 only after all the keytops 12 are mounted on the frame 11. Thus, in conventional notebook type personal computers, the top faces of the plural keytops 12 become slanted and are arranged in corrugated multiple stages, which cause the problem that the character printing is troublesome and exhibits a poor yield.